The invention relates to a brake-pressure-transmitter (master cylinder) arrangement for a hydraulic motor-vehicle brake system according to the preamble of Patent claim 1 and to a brake system equipped therewith.
It is generally known that, in hydraulic brake systems for motor vehicles, the brake-pressure-transmitter arrangement comprises a so-called master cylinder in order to produce a brake pressure for the wheel brake, this brake pressure being proportional to the actuating force introduced via the input member--normally a brake pedal. Furthermore, it is generally known to also equip the brake-pressure-transmitter arrangement with a brake booster, which provides an auxiliary force in order to amplify the actuating force introduced via the brake pedal. Suitable brake boosters are both pneumatic boosters, which work according to the vacuum principle, and hydraulic boosters, which work with a hydraulic pump.
DE 28 45 794 C2, for example, discloses such a pneumatic brake booster, whereas DE 44 43 869 A1, for example, discloses a hydraulic brake booster. Both the pneumatic and the hydraulic brake boosters have a movable wall, which divides an inner housing space into two chambers and transmits a force via an output member to the master cylinder when the chambers are subjected to a pressure difference as a function of a force effective at the input member. In the non-actuated state the chambers are pressure-balanced, so that the movable wall transmits no force to the output member. In the pneumatic booster, the pressure difference is produced by a vacuum being produced in one chamber by means of a vacuum source, whereas atmospheric pressure is applied to the other chamber. In contrast, the pressure difference in the hydraulic booster is produced by means of a hydraulic pump, the suction side-of which is connected to one chamber and the pressure side of which is connected to the other chamber, so that the hydraulic pump delivers in the direction from one chamber to the other chamber in order to obtain brake-force amplification.
Nonetheless, such a hydraulic brake system is worth improving, since the use of a generally known brake booster requires a relatively large installation space in the motor vehicle.
Furthermore, when a pneumatic brake booster is used, a vacuum source must be provided in the motor vehicle. Although the vacuum produced in the intake duct may be utilized in principle in a vehicle equipped with a spark-ignition engine, however, pronounced fluctuations of the vacuum produced in this way may adversely affect the performance of the brake system, in particular with regard to the constantly increasing performance requirements, so that outlay and costs for the provision of an independent vacuum source are inevitable.
A disadvantage with the use of a known hydraulic booster may be that additional valve arrangements, electromagnetically actuated as a rule, are necessary in order to ensure a pressure compensation for all chambers and working spaces, including those of the wheel brakes, when the brake-pressure-transmitter arrangement is not actuated. This also results in outlay and costs.